A further confirmation comes from the distant past. Around A.D. 180, Irenaeus, Bishop of Lyon in what was then Roman Gaul, wrote a massive treatise called Against Heresies. The book was a fierce denunciation of all those whose views about Jesus and his message differed from those of the mainstream church. Among those he attacked was a group who revered Judas, "the traitor,” and had produced a “fictitious history,” which "they style the Gospel of Judas.”

Decades before the fragile manuscript in Kasser's hands was written, the angry bishop apparently knew of the original Greek text.

Irenaeus had plenty of heresies to contend with. In the early centuries of Christianity, what we call the church, operating through a top-down hierarchy of priests and bishops, was only one of many groups inspired by Jesus. Biblical scholar Marvin Meyer of Chapman University, who worked with Kasser to translate the gospel, sums up the situation as “Christianity trying to ﬁnd its style.”

For example, a group called the Ebionites maintained that Christians should obey all Jewish religious laws, while another, the Marcionites, rejected any connection between the God of the New Testament and the Jewish God. Some said that Jesus had been wholly divine, contradicting those who insisted he was completely human. Yet another sect, the Carpocratians, allegedly indulged in ritualized spouse swapping. Many of these groups were Gnostics, followers of the same strain of early Christianity reflected in the Judas gospel.

"Gnosis means 'knowledge' in Greek,” Meyer explains. The Gnostics "believed that there is an ultimate source of goodness, which they thought of as the divine mind, outside the physical universe. Humans carry a spark of that divine power, but they are cut off by the material world all around them”—a flawed world, as the Gnostics saw it, the work of an inferior creator rather than the ultimate God.

While Christians like Irenaeus stressed that only Jesus, the son of God, was simultaneously human and divine, the Gnostics proposed that ordinary people could be connected to God. Salvation lay in awakening that divine spark within the human spirit and reconnecting with the divine mind. Doing so required the guidance of a teacher, and that, according to the Gnostics, was Christ’s role. Those who grasped his message could become as divine as Christ himself.

Hence Irenaeus’s hostility. "These people were mystics,” says Meyer. "Mystics have always drawn the ire of institutionalized religion. Mystics, after all, hear the voice of God from within and don't need a priest to intercede for them.” Irenaeus began his book after he returned from a trip and found his flock in Lyon being subverted by a Gnostic preacher named Marcus, who was encouraging his initiates to demonstrate direct contact with the divine by prophesying. Hardly less outrageous was Marcus’s evident success with women in the flock. The preacher’s "deluded victim,” wrote Irenaeus indignantly, "impudently utters some nonsense” and “henceforth considers herself to be a prophet!”